1. Field of the Invention
This invention relates to liquid recording medium suitable for use in a recording method which performs image recording by ejecting and spattering the liquid recording medium in the form of droplets from an orifice of a nozzle onto a recording member. More particularly, the invention is concerned with a novel liquid recording medium with various properties of remarkable improvement such as stability and responsiveness of the droplets at their ejection from the discharge orifice, stability in storage over a long period of time, affinity for recording members, quality of the image to be recorded, and so forth.
2. Description of Prior Art
So-called non-impact recording methods have recently drawn public attention, because uncomfortable noises during the recording operation could be reduced to a negligible order. Among these particularly important is the so-called ink jet recording method which allows high-speed recording on a plain paper without particular image-fixing treatment, and, in this particular field, there have been proposed various approaches including those already commercialized, and others still under development.
Such ink jet recording method is to perform recording by spattering the liquid recording medium, or the so-called "ink", in the form of droplets and adhering the same onto the recording member. The recording medium to be used for such recording method is usually composed, as its principal constituent, of a recording agent (various sorts of dyestuff and pigment) to form a recorded image which is dispersed or dissolved in water, organic solvent, or a mixture of these. When some treatment is rendered onto the recording member to form color at the time of the recording on such recording member, the liquid recording medium may sometimes be composed only of water, organic solvent, or a mixture thereof, without inclusion of the various sorts of dyestuff and pigment. Such ink jet recording can be classified into several processes according to the method of generating the droplets and also to the method of controlling the direction of spattering of the droplets. In either system, the liquid recording medium is required to have various physical parameters such as viscosity, surface tension, electric conductivity, etc. in conformity to the method of generating the droplets and controlling method of the spattering direction of the droplets.
In the following, one example of such recording device will be explained. It is not always necessary that the liquid recording medium is in the form of droplet immediately after the liquid recording medium leaves the orifice. It may leave the orifice in the form of liquid flow, but the liquid recording medium should be in the form of droplet at least when it reaches the recording member.
FIG. 1, for example, illustrates a device which performs recording by applying a recording signal to a recording head having a piezo-vibrator, and by generating droplets of the liquid recording medium in accordance with the recording signal. In the drawing, a reference numeral 1 designates the recording head having the piezo-vibrator 2a, a vibrating plate 2b, an inlet 3 for the liquid recording medium, a chamber 4 defined within the head and a discharge orifice 5. For the purpose of increasing the recording speed, a plurality of such recording heads are provided in some case. Into the chamber 4, the liquid recording medium 7 stored in a storage tank 6 is supplied through a supply pipeline 8a. On the half way of the supply pipeline 8a, there is sometimes provided an intermediate device 9 such as a pump or a filter. Between the piezo-vibrator 2a and the vibrating plate 2b, a recording signal S which has been converted into pulses by a signal processing device (e.g., a pulse converter) is applied, in accordance with which signal a pressure change occurs in the liquid recording medium within the chamber 4. As the result of this, the liquid recording medium 7 is discharged from the discharge orifice 5 in the form of droplets 11, and informations are recorded on the surface of the recording member 12. Incidentally, there are various modified types of such recording device, wherein number and shape of the chamber 4 of arrangement of the piezo-vibrator 2a are varied.
FIG. 2 is a modified type of the recording device shown in FIG. 1, wherein the chamber 4 is constructed with a cylindrical glass tube, on the outer periphery of which a cylindrical piezo-vibrator 2a' is disposed. The droplet discharge principle of this recording device is the same as that shown in FIG. 1.
FIG. 3 shows another example of the recording device which performs recording by continuously generating droplets of the liquid recording medium, e.g., a device, in which the droplets are electrically charged in accordance with a recording signal, and thereafter the spattering direction of the droplets is controlled by deflecting electrodes (which are applied with a uniform electric field) to perform the recording. In this type of the device, a portion of the liquid recording medium which has not been used for the recording operation is recovered for re-use. In FIG. 3, reference numerals 1 to 12 and a reference symbol S designate the same component elements as those shown in FIG. 1, while numeral 8b refers to a recovering pipe for the liquid recording medium to be recovered without being used for the recording, a numeral 13 designates a pulse generator for generating droplets of the liquid recording medium, 14 refers to electrodes for charging the droplets of the liquid recording medium, 15 designates deflecting electrodes, 16 a power source, 17 droplets to be used for the recording, 18 droplets not used for the recording, 19 a recovery gutter, and 20 a recovery and storage tank for the recovered liquid recording medium.
For instance, when the recording device of the type shown in FIG. 1 is used, it is necessary that viscosity, surface tension, etc. of the liquid recording medium be in appropriate ranges. Since, also, the discharge orifice is an extremely fine port (usually in a range of 20 to 200 .mu.m in diameter), the liquid recording medium should possess, as its important requirements, such properties that does not generate solidified substance during stoppage of the recording operation or storage of the liquid recording medium, which becomes liable to clog the orifice, and that is difficult to change its chemical properties or physical parameters, and others. Or, the liquid recording medium is also required to contain therein sufficient quantity of component for the recording agent so that a recorded image may exhibit high image contrast, to be excellent in its affinity for various kinds of recording members, and to be satisfactory in its penetrating and fixing properties.
With a view to satisfying such various conditions, there have heretofore been made various proposals. For instance, U.S. Pat. No. 4,106,027 discloses a liquid recording medium having a low viscosity of 5 c.p. or below and an electrical conductivity of 10.sup.-4 ohm.sup.-1 cm.sup.-1 or above, and which is principally composed of an organic solvent. The liquid recording medium is used in a recording device of a type as shown in FIG. 3, in which the droplets are charged. For the organic solvent, the prior patent uses, as its principal component, alkane or cycloalkane having the carbon content of from 5 to 8, lower alcohols, ethers (diethylether, dioxane, tetrahydrofuran), aromatic hydrocarbons, halogenated hydrocarbons, or esters.
On the other hand, there have also been known many kinds of liquid medium component system containing water. For example, U.S. Pat. No. 3,687,887 discloses an aqueous system liquid recording medium consisting of an organic resin binder such as styrene-maleic anhydride, etc., ether of polyhydric alcohol (particularly, glycol), and a coloring agent (carbon black and dyestuff suspended in water) so as to obtain a recorded image having high image density and good image-fixing property on the image forming base such as gelatin, resin film, etc.
Further, U.S. Pat. No. 3,705,043 teaches a liquid recording medium consisting of a coloring agent (carbon black and nigrosine dyestuff dispersed in water), a wetting agent (polyhydric alcohol, alkyl ether of polyhydric alcohol, or a mixture thereof), and water, with a view to obtaining an infrared ray absorptive image, exhibiting appropriate viscosity value over a long period of time, and not bringing about clogging of the discharge orifice.
U.S. Pat. No. 3,776,742 discloses an effective liquid recording medium having electric conductivity and surface tension of 35 to 70 dyn/cm, and consisting of a water soluble dyestuff, an electrically conductive substance (metal chlorides, etc.), a low molecular weight polyol, and a crystalline organic compound such as urea, etc. This aqueous system liquid recording medium is effective in quick image-fixing on a recording member such as paper which contains therein cellulose.
However, it is considerably difficult to obtain the liquid recording medium capable of satisfying simultaneously those various requirements as mentioned above, there still remain various points to be improved. For example, the liquid recording medium with an organic solvent as its principal constituent satisfies the indispensable condition to generate the droplets from a fine discharge orifice with favorable stability and responsiveness (in accordance with the hydrodynamic condition), i.e., a low viscosity (generally, 10 c.p. or below). However, many of the organic solvents have generally high volatility which tends to produce solid substance, and such solid substance is liable to clog the discharge orifice. The surface tension is also a factor to influence the discharge stability and responsiveness of the droplets, same as the viscosity, hence it should preferably be as large a value as possible. The value of the surface tension in the organic solvents, however, is considerably low in comparison with water (most of them usually have the surface tension of 25 dyn/cm or below). Further, while penetration of the liquid recording medium into the recording member (such as paper) is satisfactory, it has various disadvantages such that it produces remarkable running in the resulted image, hence low image resolution, and is poor in its dissolving stability of the components in the recording agent, hence sufficient quantity of the recording agent is difficult to be incorporated in the liquid recording medium, etc.
On the other hand, the penetrating the image-fixing properties of the liquid recording medium consisting of water as the principal constituent depend its penetrating and image-fixing properties upon the degree of sizing and gas permeability of the recording member. In case the recording is done on the recording member having high degree of sizing, the resulted image is prone to be thin or broken. In case a colored image is to be obtained, faithful color tone is difficult to be reproduced due to mixing of the liquid recording mediums of different color tones with the consequent lowering of the image resolution, and other inconveniences. With a view to improving such disadvantages, it has so far been a general practice to select a specific recording member having a low degree of sizing, although such recording member is not so practical in that it is not suitable for general purpose use. Moreover, there also exist such disadvantages that not only the water-resistant property of the recorded image is inferior, but also, when polyhydric alcohol is added to prevent the discharge orifice from clogging due to evaporations of water, if such polyhydric alcohol is incorporated to such an extent that the clog preventive effect can be attained to a satisfactory extent, the physical parameters such as viscosity, surface tension, etc. are difficult to be maintained in appropriate ranges, and temperature dependency of the physical parameters increases.
These are the factors to lower the printing characteristics of the liquid recording medium.
Under such circumstances, there have been strong demands for development of practical liquid recording medium capable of simultaneously satisfying the above-mentioned various conditions, being excellent in its recording property, and being suited for general purpose use. The present invention has been made in view of the afore-described various points of problem and as the result of studying from the abovementioned standpoints.